Refrigerator with defrost when necessary system



Dec. 26, 1967 R. s. HANSON 3,359,750

REFRIGERATOR WITH DEFROST WHEN NECESSARY SYSTEM I Filed Dec. 2, 1965 4Sheets-Sheet l INVENTOR. Robert 5. Hanson His Arforney Dec. 26, 1967 R.s. HANSON 3,359,750

REFRIGERATOR WITH DEFROST WHEN NECESSARY SYSTEM Filed Dec. 2, 1965 4Sheets-Sheet 2 INVENTOR. Robert 5. Hanson ya 5W His AI/om e y R. s.HANSON 3,359,750

REFRIGERATOR WITH DEFROST WHEN NECESSARY SYSTEM Dec. 26, 1967 4Sheets-Sheet Filed Dec. 2, 1965 INVENTOR. Robert 5. Hanson BY jgumm HisAttorney R. s. HANSON 3,359,750

REFRIGERATOR WITH DEFROST WHEN NECESSARY SYSTEM Dec. 26, 1967 4Sheets-Sheet 4 Filed Dec. 2, 1965 l no Fig. 6

. INVENTOR. Robert 5. Hanson His A Ham 6 y Y United States Patent3,359,750 REFRIGERATOR WITH DEFROST WHEN NECESSARY SYSTEM Robert S.Hanson, Dayton, Ohio, assignor to General Motors Corporation, Detroit,Mich., a corporation of Delaware Filed Dec. 2, 1965, Ser. No. 511,098 13Claims. (Cl. 62-456) ABSTRACT OF THE DISCLOSURE In preferred form, arefrigerator including above and below freezing compartments, anevaporator compartment, an evaporator coil in the evaporator compartmenthaving an integral fin and tube configuration wound to present anincreased cross-sectional flow area through the center of the evaporatorcompartment to prevent undesirable reduction of air flow through thecompartment following frost build-up on the evaporator coil andincluding a defrost when necessary control having a first powerdiaphragm responsive to the skin temperature of the evaporator coil andthe temperature of an interior part of the compartment and furtherhaving a second power diaphra-gm responsive to ambient conditions aboutthe refrigerator for modulating the control action in accordance withambient temperature variations.

This invention relates to frost-proof refrigerators and moreparticularly to an improved evaporator assembly for cooling air beingcirculated in frost-proof refrigerators.

Frost-proof refrigerators generally are characterized by a primary aircirculation system that includes an evaporator enclosure forming anevaporator compartment separate from the above and/or below-freezingcompartments through which the primary air stream is circulated. Therecirculated primary air stream draws moist air from the respectivefreezing compartments across an evaporator located within the evaporatorcompartment and the moisture in the recirculated air is deposited asfrost on the evaporator member so as to be removed from the air stream.By virtue of this type of system, there is little or no frost buildup inthe primary food storage compartments of a refrigerator or the like thatrequires periodic removal by the housewife.

While frost-proof refrigerators solve the problem of frost buildup inthe food storage compartments and especially in the below-freezingcompartment of a refrigerator, it is necessary to include a provision insuch systems to defrost the evaporator when it becomes coated with afrost buildup that will reduce the desired air flow pattern for coolingin the freezing compartments of the refrigerator or a frost buildup thatwill reduce the cooling effectiveness of the evaporator.

In the past, the primary air flow was passed through or acrossevaporator members that have been characterized as having rather asubstantial number of separate fins directed across the air flowpassageway. In order to provide a sufficient heat transfer surfacebetween the evaporator and the recirculated air, the number of finsnecessarily has been relatively substantial and the spacing between thefins has been of a relatively reduced nature to provide suflicient finsurface on the evaporator member.

One problem in such frost-proof systems has been to maintain a desiredair flow across the evaporator in the evaporator compartment as frost isdeposited thereon and, furthermore, to remove periodically the frostbuilt up on the evaporator section when the frost buildup reduces thecooling effectiveness of the evaporator member.

Accordingly, an object of the present invention is to improvefrost-proof refrigerators by the provision therein 3,359,750 PatentedDec. 26, 1967 "ice of an improved evaporator arrangement for cooling theprimary air cooling stream through the frost-proof refrigerator by theprovision of a three-piece evaporator including a helically Woundintegral fin and tube member that forms an opened central region throughthe evaporator for the uninterrupted passage of air therethrough andwherein infrared heater means are located within the opened passagewaythrough the helically wound integral fin and tube for removing frosttherefrom by radiant heat transfer from said heating means rather thanconduction through said evaporator.

A still further object of the present invention is to improvefrost-proof refrigerators having a primary air circulating systemincluding refrigerant means for cooling the air stream by the provisionof an improved evaporator arrangement including a helically woundintegral fin and tube member having a central opened region therethroughdefined by a plurality of fins directed interiorly of said coil with endportions thereon located in spaced apart relationship with one anotherthrough a distance in excess of the length of the fins whereby theprimary air circulation can pass through said evaporator following afrost buildup on the fins.

Still another object of the present invention is to improve frost-proofrefrigerators having above and belowfreezing compartments and means forcirculating a cold air stream through said compartments by the provisionof an improved evaporator arrangement for cooling the circulating airand removing moisture therefrom including a helically coiled integralfin and tube evaporator member having a first plurality of passeslocated in a common plane and a second plurality of passes located in acommon plane spaced apart from that of the first plurality of passes andwherein the plurality of passes each includes a large number of integralfins directed interiorly of the helical coil to form an open spacehaving a width equal to that of the passes and a depth greater than thelength of the fins to direct the circulating primary air stream throughthe helically coiled evaporator member in good heat transferrelationship with all portions thereof irrespective of a frost buildupon the fins thereof.

A further object of the'invention is to improve a frostproofrefrigeration system of the type set forth in the preceding objectwherein the helically coiled evaporator member includes side wallmembers for forming open space within an evaporator compartment oneither side of the helical coil and wherein means are included to directair through said side walls interiorly of said coil downstream of theinlet end of said coil to improve the distribution of frost on saidcoil.

'A still further object of the present invention is to improvefrost-proof refrigerators of the type including a primary coldcirculation system for passing moist air in heat transfer relationshipwith an evaporator for cooling the air stream and removing frosttherefrom by the provision of an automatic defrosting system includinginfrared heating means for removing frost from the evaporator by directradiant transfer to the evaporator wherein the heating means includes anelectrically energizable high-temperature resistance element selectivelyconnected across a power source by thermally responsive switch meansincluding a diaphragm actuator associated with a thermally responsivebulb element including a first portion located in direct heat transferrelationship with the coldest portion of the evaporator member and asecond portion located in heat transfer relationship with inlet air tothe evaporator member whereby when the first bulb portion senses a firstpredetermined temperature, a defrost cycle is initiated, and when thesecond bulb portion senses a second predetermined temperature, thedefrost cycle is automatically terminated.

Yet another object of the present invention is to improve defrostsystems =of the type set forth in the preceding object by the provisionof a helically coiled integral fin and tube evaporator member having aplurality of fins directed interiorly of the coil and located in spacedrelationship from one another to form an open space centrally of andthrough the coil in which said infrared heating means i located.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being had to the accompanyingdrawings wherein :a preferred embodiment of the present invention isclearly shown.

In the drawings:

FIGURE 1 is a fragmentary view in vertical section of the improvedevaporator arrangement shown in association with a plural compartmentfrost-proof refrigerator and a diagrammatically illustrated refrigerantsystem;

FIGURE 2 is an enlarged view in horizontal section taken through theimproved evaporator arrangement;

FIGURE 3 is a view, partially in section and partially in frontelevation, of the improved evaporator arrangement;

FIGURE 4 is an enlarged view in vertical section of a portion of aninfrared energy source in the improved arrangement;

FIGURE 5 is an enlarged view in vertical section taken along the line5-5 of FIGURE 3; and

FIGURE 6 is a diagrammatic showing of a control system for the presentinvention.

Referring now to FIGURE 1, a frost-proof refrigerator 10 is illustratedincluding an outer cabinet 12 and an inner liner 14 having a layer ofthermal insulation 16 therebetween. The inner liner 14 is traversed byan insulated divider partition 18 that forms an above-freezing foodstorage compartment 20 and a below-freezing food storage compartment 22within the inner liner 14. Access openings 23, 24 are provided in theinner liner 14 to the compartments 20, 22, respectively. In theillustrated arrangement, the opening 23 is closed by a vertically hingedbottom door 25 and the opening 24 is closed by a vertically hinged topdoor 26.

Forwardly of the rear wall of the inner liner 14 is located a rearbafile or shroud 27 in which is located a primary air circulatingcentrifugal fan 28 driven by a motor 30 located within the insulation 16of the rear wall of the refrigerator 10. The fan 28 directs air througha passageway 32 formed by the shroud 27 and the rear wall of the liner14 interiorly of the freezer compartment 22 and through a passageway 34formed by a lower portion of the shroud 27 and the rear wall of theliner 14 into the above-freezing compartment 20. The passageway 34 has adamper 36 located therein that is pivotally supported on the baffle 27for manual adjustment to proportion the air flow through the passageways32, 24, respectively, depending upon the amount of cooling desired inthe above-freezing compartment 20.

Within the below-freezing compartment 22 is located a bottom freezerpanel 38 that forms an evaporator compartment 40 in cooperation with adownwardly bent portion of the insulated partition panel 18. Across thefront edge of the panel 38 is located an air return member having aplurality of openings 42 therein for returning circulated air from thebelow-freezing compartment 22 interiorly of the evaporator compartment40 and the divider partition 18 has a plurality of openings 44 thereinto direct return air from the above-freezing compartment 20 into theevaporator compartment 40. The panel 38 in cooperation with therearwardly located shroud 27 forms an inlet opening 46 to therecirculating fan 28 which draws return air from the openings 42, 44through the evaporator compartment 40 to be discharged through thedischarged passageways 32, 34, respectively.

The above-described recirculating primary air stream is cooled by animproved evaporator arrangement 48 within the evaporator compartment 40that has a refrigerant accumulator 47 connected by a conduit 49 to thesuction side of a refrigerant compressor 50 that directs compressedrefrigerant through a condenser 51 thence through a suitable refrigerantexpansion means representatively shown as being an expansion valve 52,thence through a conduit 54 connected to the inlet end of the evaporator48.

More particularly, and as best seen in FIGURES 2, 3 and 5, the improvedevaporator 48 is of a low-cost, threepiece construction including ahelically coiled integral fin and tube evaporator member 56 having afirst plurality of lower passes 58 located in a comon plane adjacent adrip pan 55 supported on the insulated divider partition 18 under themember 56 to collect water defrosted therefrom. Member 56 also includesa second plurality of passes 68 located in a common plane closelyadjacent the panel 38. The lower and upper passes 58, 60 are joined byreturn bend portions 62. Each of the passes 58, 60 includes a pluralityof integral fins 64 directed outwardly of the coiled member 56 havingthe ends thereof spaced apart from the drip pan 58 and the panel 38,respectively. Each of the return bends 62 includes a plurality ofradially outwardly directed fins 66 on the outer radius thereof and aplurality of collapsed fins 68 on the inner radius thereof that preventundesirable bending of the return bend portions 62.

Furthermore, the lower and upper reaches 58, 60 each includes aplurality of integral fins 70 thereon directed interiorly of the coiledmember 56 and having their ends spaced apart to form a central opening72 from the end of the coiled member 56 located immediately downstreamof the return openings 42, 44 into the evaporator compartment 40 and theend of the coiled member 56 that is located immediately upstream of theinlet opening 46 to the recirculating fan 28.

The evaporator arrangement 48 further includes spaced apart side members74, 76 each having a generally U.- shaped configuration and edgeportions thereof that engage, respectively, the panel 38 in thebelow-freezing compartment 22 and the upper surface of the drip pan 55.As best seen in FIGURE 5, each of the side members 74, 76 includes aplurality of spaced apart openings 78 in which are located one of thereturn bend portions 62 whereby the coiled member 56 is located withinthe evaporator compartment 40 with the outer fins 64 thereon spaced asmentioned above and the central opening 72 through the coiled member 56being located generally centrally of the evaporator compartment 40 inserial air flow relationship with the return openings 42, 44 and theinlet opening 46 to the recirculating fan 28.

As best seen in FIGURE 2, each of the side members 74, 76 are spacedinwardly of the inner liner 14 on the side walls of the refrigerator 10to form therewith passageways 80, 82 on either side of the coiledevaporator member 56, a block of insulating material 84- is locatedbetween the inner liner 14 on one side of the coiled member 56 and theend of the side member 74 located closest to the inlet opening 46 toprevent air fiow through the passageway from the return openings 42, 44and the inlet 46 to the recirculating fan 28. Likewise, a block ofinsulating material 86 is located between the liner 1.4 on the oppositeside wall and the like end of the side member 76 to prevent direct airflow from the return openings 42, 44 and inlet 46 of the fan 28 throughpassageway 82.

Each of the side members 74, 76, however, includes openings 88 betweenthe return bend portions 62 supported therein that will direct airthrough the sides of the helically coiled evaporator member 56 into theinterior space 72 thereof.

By virtue of the above illustrated arrangement, when the circulating fan28 is running, air will be discharged into the freezing compartments 20,22, respectively, where moisture is picked up so as to prevent anundesirable frost buildup in the compartments and especially in thebelow-freezing compartment 22. The moist air is returned throughopenings 42, 44 into the evaporator compartment 40 and distributedthrough a first path directly into the central opening 72 and the upperand lower spaces between the helical coil 56 and the panel 38 and drippan 55 to pass serially across the helically coiled evaporator member 56into the inlet opening of the fan 28.

By virtue of the above illustrated arrangement, namely the provision ofa helically coiled integral fin and tube member of the type set forthabove, the air flow between the return openings 42, 44 and the fan inletopening 46 will pass through a substantial open area in which no finsare located. As a result, as frost builds up on the fins, there will bea tendency to prolong the period during which time air will freely passthrough the evaporator member before being undesirably restricted by thefrost buildup so as to reduce the air flow through the freezingcompartments to a degree Where the desired temperature levels thereinwill be reduced in an undesirable fashion.

In addition to the relative open configuration of the helically coiledintegral fin and tube member 56, the evaporator assembly 48 is furthercharacterized by the inclusion therein of an improved infrared energyheater assembly 90 that includes an open ended tubular enclo sure 92 ofa suitable infrared transmissive material, such as quartz, which hasopposite end portions thereon directed respectively through an opening94 intermediate the ends of each of the side members 74, 76. The tubularenclosure 92 has a high-temperature electrical resistance element 96directed therethrough having the opposite ends connected to a maleterminal member 98 that is received within a female terminal 100 havinga lead line 102 connected thereto. A tubular cap 104 fits over each openend of the tubular member 92 and the terminal 100, as best seen inFIGURE 4, to prevent the entrance of moisture into the interior of thetubular member 92. An opening 105 in the cap 104 vents the interior ofenclosure 92.

The heater assembly 90' is located in the central open space 72 throughthe helical coil 56 and is disposed slightly forwardly of the coil 56 inthe illustrated arrangement to be located in direct radiant heattransfer relationship with most of the fins on the forwardly locatedpasses 58, 60 of the coiled member 56 for removing frost builduptherefrom when the heater assembly is energized. Since the helicallycoiled member 56 has a relatively open configuration between the finportions thereof, the energy output from the infrared heater assembly 90is able, through direct radiant heat transfer, to remove most of thefrost buildup therefrom in a highly eflicient manner.

The system of defrosting by infrared energy is generally known but inthe illustrated arrangement, the combination of the single tubularformed heating assembly and the helically coiled member 56 ischaracterized by the fact that a relatively opened air flow path ismaintained in the evaporator compartment which is desirable in afrost-proof refrigerator for the reasons set forth above and,furthermore, affords an open path between the heater assembly 90- andthe fins thereon for direct radiant defrosting.

In accordance with certain other principles of the present invention,the heater assembly 90 is periodically energized by automatic controlmeans to initiate a defrost cycle that is operated without the need fortimers, frost detectors or other mechanical devices. The system iseconomical in construction and utilizes a combination of the temperatureof the coldest portion of the evaporator coil, represented in theillustrated arrangement by the accumulator 47, and a means for sensingthe temperature of the return air from the food storage compartments.

More particularly, in FIGURE 6- the improved control arrangement isillustrated as including a double-throw, single-pole switch 106 that iselectrically connected at one end thereof to a Wire L of a suitablepower source. The switch 106 is operatively positioned by a firstbellows assembly 108 that is fluidly connected to a capillary tube 110including a thermally responsive fluid. The capillary tube 110 has afirst coil portion 112 thereof located in the return air flow from theabove and below-freezing compartments 20, 22, as best seen in FIGURE 2.The capillary tube 110 further includes a second coil portion 114 thatis serially arranged with the first portion 112 and located in directheat transfer contact with the outer surface of the accumulator 47, asbest seen in FIGURE 2, which, in the illustrated system, represents thecoldest region on the evaporator coil 56.

The switch 106 is further operatively positioned by a second bellows 116that is in communication with a thermally responsive fiuid filledcapillary tube 118 that has a bulb portion 120 located in a suitableregion of the refrigerator for sensing ambient temperatures in which therefrigerator operates.

A contact 122 of the switch 106 during a cooling cycle of operation ofthe refrigerator is positioned in electrical contact with a contact 124that is electrically connected to a conductor 126 which connects a motor128 for driving the compressor to wire L of the power source. A fanmotor 129 is connected in parallel across motor 128 to be simultaneouslyenergized. During a defrost cycle of operation, the switch 106 is movedso that the contact 122 thereof electrically connects to a contact 130which is electrically connected to one of the terminals 102 from thehigh-temperature resistance element 96 that has the opposite end thereofelectrically connected to the wire L The switch 106 thus can becharacterized as one that will automatically interrupt the refrigerationcycle and start a heating or defrost cycle in response to thermalconditions within the evaporator compartment 42. It is recognized thatwhen an evaporator coil becomes covered with frost, as in the case of anevaporator portion in a frostproof refrigerator, the amount of heattransferred to the refrigerant in the coil in a given period of timewill be reduced. Since the condenser and compressor have a reduced heatload, the back pressure in the system will be reduced and also thetemperature of the refrigerant coil 56 will be lowered. It is alsorecognized that the reduction in the back pressure and the evaporatorcoil skin temperature under reduced loads, as occurs upon frosting up ofthe coil, is dependent in part upon the ambient conditions in which therefrigerator is being operated.

In addition to the reduced heat load produced by a frost buildup, insingle evaporator frost-proof refrigerators of the type underdiscussion, as the air passageways through the evaporator become blockedwith frost, there is a consequent reduction in air flow and, therefore,a lesser heat transfer to the refrigerant coil than is normally thecase. The combination of the reduction of heat transfer produced byfrost buildup and that produced by a reduction in air flow will producea substantial reduction in the skin temperature of the accumulator 47which will cause the thermally responsive fluid in the capillary tube110- to condense whereby the bellows 108 will position the contact 122to complete the energization circuit of the heater 96. When this occurs,the energization circuit for the compressor motor 128 is terminated.Radiant energy from the heater assembly 90, whether by direct radiationheat transfer or by reflective heat transfer off the panel 38 of thefreezer compartment 22 and the drip pan 55, will be directed against thefrost build up on the fins 64, 70 of the helical coil 56 to cause it tomelt and flow into the drip pan 55 for removal through a suitable draintube (not shown). During the defrost cycle of operation, the centrifugalfan 28 is de-energized to prevent an undesirable transfer of heated airinto the compartments 20, 22.

In order to assure that the defrost cycle will be of a sufiicientduration to remove the frost buildup on the coil 56-, the controllerincludes the coil portion 112 in the capillary tube 110 at a point inthe evaporator com- 75 partment 42 which has the temperature thereofincreased at a lesser rate than does the temperature increase in thecoil 56 and accumulator 47. Thus the coil portion 112 can becharacterized as a defrost terminating bulb which is heated more slowlythan the coil 114 to produce a predetermined lag in the opening movementof the contact 122 from the contact .130. When a predeterminedtemperature is attained, the switch 106 will be positioned by thebellows 108 to open the energization circuit for resistance 96 and tocomplete the energization circuit for the compressor motor 128 to starta new refrigeration cycle.

The ambient compensating bellows 116 will bias the switch 106 so thatthe defrost cycle will be initiated at varying accumulator skintemperatures in accordance with the ambient temperature under which therefrigerator is operating. For example, in the illustrated arrangement,the switch 106 will initiate a defrost cycle under 110 F. ambientconditions when the evaporator coil reaches 12" F. Under 90 ambientconditions, the defrost cycle is initiated at an evaporator oraccumulator skin temperature of 16 F. and at ambient conditions of 70F., the defrost cycle is initiated when the bulb 114 senses skintemperature in the neighborhood of 20 F. The ambient compensationenables the automatic defrost system to remove frost from the coil in aneffective fashion through a wide range of operating conditions. Withoutsuch ambient compensation, the automatic defrosting arrangementillustrated might initiate a defrost cycle before the frost buildup onthe coil 56 occurs that needs defrosting.

While the embodiment of the present invention as herein disclosedconstitutes a preferred form, it is to be understood that other formsmight be adopted.

What is claimed is as follows:

1. A frost-proof refrigerator comprising insulating means forming abelow-freezing compartment and an above-freezing compartment, enclosuremeans forming an evaporator compartment separated from said freezingcompartments including an inlet opening and an outlet opening, means forcirculating air from said below and above-freezing compartments throughsaid inlet of said evaporator compartment thence through the outlet ofsaid evaporator compartment, said fluid circulating means including arecirculating fan having its inlet in communication with the outlet ofsaid evaporator compartment, a helically coiled integral fin and tubeevaporator member located in said evaporator compartment between theinlet and outlet ends thereof, said helically coiled evaporator memberincluding a first plurality of passes located in .close spacedrelationship with one surface of said evaporator enclosure means and asecond plurality of passes located in close spaced relationship withanother surface of said evaporator enclosure means, a plurality ofreturn bend portions for joining said first and second plurality ofpasses and locating said passes apart from one another to form arelatively open air passageway therebetween, said plurality of passeseach including a plurality of integral fins thereon directed interiorlyof said outlet of said evaporator compartment, said passageway throughsaid helically coiled member communicating directly with the inlet endof said evaporator compartment for receiving return air from said aboveand below-freezing compartments, and means within said evaporatorcompartment for directing a predetermined portion of the return air fromsaid above and below-freezing compartments interiorly of said helicallycoiled integral fin and tube evaporator tmember through the sidesthereof for improving the pattern of frost deposition on said evaporatormember during the operation of the refrigerator.

2. A frost-proof refrigerator including insulating means forming abelow-freezing compartment and an abovefreezing compartment, enclosuremeans forming an evaporator compartment separated from said compartmentsincluding an inlet opening and an outlet opening, means for circulatingair from said below and above-freezing compartments through the inlet ofsaid evaporator compartment thence through the outlet thereof includinga recirculating fan having an inlet opening in communication with theoutlet opening of said evaporator compartment, means for cooling airpassing through said evaporator compartment including a helically formedintegral fin and tube evaporator member having spaced apart passesdirected substantially across the width of said evaporator compartment,return bend portions for joining said spaced apart passes of saidhelical coil, said spaced apart passes of said helical coil having aplurality of integral fins formed thereon directed interiorly of saidcoil and located in spaced apart relationship with one another to forman uninterrupted fluid flow passageway between said inlet of saidevaporator compartment and the outlet thereof for free fluid flow ofreturned air from said above and below-freezing compartments followingthe deposition of frost on said fins on said passes, and defrost meansincluding a sheathed infrared emissive resistance element within saidhelically coiled evaporator member for removing frost from said integralfins through direct radiant heat transfer.

3. In the combination of claim 2, said defrost means including means forselectively controlling the energization of said resistance elementincluding a thermally responsive switch having a pair of contacts, afirst bellows for opening and closing said contacts, said bellowscommunicating with a first thermally responsive bulb means including afirst portion located in heat transfer relationship with said evaporatorfor initiating a defrost cycle of operation and a second portion thereoflocated in heat transfer relationship with the return air from saidabove and below-freezing compartments for terminating the defrost cycleof operation, a second bellows for modulating opening and closing ofsaid contacts, second thermally responsive bulb means communicating withsaid second bellows and located in heat transfer relationship with anambient temperature source for continually modulating the controllingaction of said first bellows in response to ambient temperatureconditions.

4. In the combination of claim 2, means within said evaporatorcompartment for directing a predetermined portion of the return air fromsaid above-freezing and below-freezing compartments interiorly of saidhelically coiled evaporator member downstream of the point where saiduninterrupted fluid flow passageway through said helically coiledevaporator member directly communicates with said inlet end of saidevaporator compartment. 5. In the combination of claim 4, said means fordirecting return air through said helically coiled evaporator memberincluding a pair of spaced apart side wall members supporting saidhelically coiled evaporator member within said evaporator compartment oneither side thereof, means forming openings in said side wall members indirect communication with the interior of said helically coiledevaporator member, and means within said evaporator compartment forblocking fluid flow therearound other than through the passagewaytherethrough and said side member openings.

6. In a frost-proof refrigerator the combination of, insulating meansforming a below-freezing compartment and an above-freezing compartment,enclosure means forming an evaporator compartment separated from saidfreezing compartments, means forming an inlet to said evaporatorcompartment and an outlet from said evaporator compartment, means forcirculating air from said below and above-freezing compartments throughsaid evaporator inlet and said evaporator outlet including arecirculating fan having an inlet opening in direct communication withsaid outlet opening of said evaporator compartment, means for coolingair circulated through said evaporator compartment including a helicallycoiled integral fin and tube evaporator member having an open centralregion formed by inwardly directed fins on said evaporator member, saidcentral open region directly communicating with said inlet of saidevaporator compartment and the outlet of said evaporator compartment,said open region being bounded on either side thereof by spaced apartside walls for supporting said helically coiled evaporator member withinsaid evaporator compartment, said side walls extending across saidenclosure means and defining therewith passageway means on either sideof said helically coiled evaporator member within said evaporatorcompartment, means forming openings in said side walls for communicatingsaid side flow passageways with the interior of said helically coiledevaporator member downstream of the portion of the central open regionof said helical coil that directly communicates with said inlet openingof said evaporator enclosure, fiu-id flow through said openings in saidside members serving to improve the distribution of frost on saidhelically coiled evaporator member to prevent undesirable blocking ofreturn air from above and below-freezing compartments directly into thecentral region of said helically coiled evaporator member from the inletopening in said evaporator compartment, an elongated tubular member ofinfrared transmissive material directed through the central region ofsaid helically coiled evaporator downstream of the portion thereofdirectly communicating with the inlet of said evaporator compartment, ahigh-temperature resistance element directed through said sheath ofinfrared transmissive material, means for sealing the interior of saidtubular sheath, means for selectively energizing said resistance elementfor producing infrared radiation therefrom for removing frost from saidhelically coiled evaporator through direct radiant energy transfer fromsaid infrared emissive element.

7. In the combination of claim 6, said means for selectively controllingthe energization of said resistance element including a thermallyresponsive switch having a pair of contacts, a first bellows for openingand closing said contacts, said bellows communicating with firstthermally responsive bulb means including a first portion located inheat transfer relationship with said evaporator for initiating a defrostcycle of operation and a second portion thereof located in heat transferrelationship with the return air from said above and below-freezingcompartments for terminating the defrost cycle of operation, a secondbellows for modulating opening and closing of said contacts, secondthermally responsive bulb means communicating with said second bellowsand located in heat transfer relationship with an ambient temperaturesource for continually modulating the controlling action of said firstbellows in response to ambient temperature conditions.

8. In a frost-proof refrigerator, the combination of, insulation meansfor forming an above-freezing compartment and a below-freezingcompartment, said insulating means including a horizontal divider panelbetween said freezing compartments, a plate located within saidbelowfreezing compartment and extending across the width thereof to formin cooperation with said divider panel an evaporator compartment, meansfor forming an inlet from said freezing compartments into saidevaporator compartment, means for drawing air from said evaporatorcompartment and for distributing said air into said aboveandbelow-freezing compartments, a helically coiled integral fin and tubeevaporator member located within said evaporator compartment having afirst plurality of lower passes and a second plurality of passes locatedabove said lower passes within said evaporator compartment, return bendportions for joining said upper and lower passes, said passes having aplurality of integral fins thereon directed outwardly of said helicalcoil into close spaced relationship with said plate and said dividerpanel, support members on each side of said helically coiled evaporatormember supportingly receiving said return bend portions for locatingsaid helically coiled evaporator member within said evaporatorcompartment and to locate said outwardly directed fin portions in closespaced relationship with said upper panel and divider panelrespectively, said passes each including a plurality of integr-al finsdirected inwardly of said helically coiled evaporator member, each ofsaid inwardly directed fins having inner end portions located in spacedrelationship with one another to form a central opening through saidhelical coil for the free passage of air between said inlet and outletof said evaporator compartment irrespective of frost buildup on saidevaporator member.

9. In the combination of claim 8, said upper plate being of infraredreflective material, a layer of infrared reflective material on saiddivider panel, a tubular member of infrared transmissive materialdirected through the interior of said helically coiled evaporator memberhaving the opposite ends thereof supportingly received by said sidemembers, a high-temperature resistance element located within saidtubular member, means for sealing the ends of said tubular memberagainst the entrance of moisture interiorly thereof, and means forenergizing said high-temperature resistance element into the infraredemissive range, said sheathed element being located in direct radiantheat transfer relationship with substantiallly all of said inwardlydirected fins on said helical coil for removing frost buildup therefromby radiant heat transfer.

10. In the combination of claim 8, means including said side members forforming opened spaces on either side of said helically coiled integralfin and tube evaporator member, means forming openings in said sidemembers for communicating said side spaces with the interior of saidhelically coiled member for receiving a predetermined portion of airpassing through said inlet of said evaporator compartment for improvingthe distribution of frost buildup on said evaporator member.

11. In an automatic defrost system for a frost-proof refrigerator, thecombination of, means forming an evaporator enclosure having an inletand an outlet, an evaporator coil located within said compartment, meansfor direcitng refrigerant through said evaporator coil, electricallyenergizable infrared heater means located within said evaporator coil inan opened central region formed therethrough between said inlet and saidoutlet of said evaporator compartment, means circulating air throughsaid evaporator compartment, said evaporator coil serving to removemoisture from'said circulated air, a refrigerant accumulator connectedto the outlet of said evaporator coil, means for automaticallyenergizing said infrared heater means for removing frost from saidevaporator coil by direct radiant heat transfer thereto, said circuitmeans including a thermally responsive switch for connecting saidinfrared heating means across a power source, said thermally responsiveswitch including bellow means, a thermally responsive fluid containingbulb having a first portion thereof in direct heat transfer relationshipwith said accumulator and a second portion thereof in heat transferrelationship with air passing through said inlet of said evaporatorcompartment, said bellow means responding to a predetermined temperaturesensed by said first bulb portion to condition said switch to initiate adefrost cycle of operation, said bellows means responding to apredetermined sensed temperature of said second bulb portion toterminate energization of said infrared heating means when said secondbulb portion senses a predetermined temperature of air in saidevaporator compartment.

12. In an automatic defrost system for a frost-proof refrigerator, thecombination of, means forming an evaporator enclosure having an inletand an outlet, an evaporator coil located within said compartment, meansfor directing refrigerant through said evaporator coil, electricallyenergizable infrared heater means located within said evaporator coil inan opened central region formed therethrough between said inlet and saidoutlet of said evaporator compartment, means circulating air throughsaid evaporator compartment, said evaporator coil serving to removemoisture from said circulated air, a refrigerant accumulator connectedto the outlet of said evaporator coil, means for automaticallyenergizing said infrared heater means for removing frost from saidevaporator coil by direct radiant heat transfer thereto, said circuitmeans including a thermally responsive switch for connecting saidinfrared heating means across a power source, said thermally responsiveswitch including bellow means, a thermally responsive fluid containingbulb having a first portion thereof in direct heat transfer relationshipwith said accumulator and a second portion thereof in heat transferrelationship with air passing through said inlet of said evaporatorcompartment, said bellow means responding to a predetermined temperaturesensed by said first bulb portion to condition said switch to initiate adefrost cycle of operation, said bellow means responding to apredetermined sensed temperature of said second bulb portion toterminate energization of said infrared heating means when said secondbulb portion senses a predetermined temperature of air in saidevaporator compartment, thermally responsive means for sensing ambienttemperature and including means for controlling said thermallyresponsive switch to delay defrost initiation upon a reduction inambient temperature.

13. An improved evaporator assembly for association with a frost-proofrefrigerator comprising, enclosure means forming an evaporatorcompartment having an inlet opening and an outlet opening, an evaporatormember disposed Within said evaporator compartment, said evaporatormember including a first and a second plurality of passes located inspaced apart relationship with one another, said first plurality ofpasses being located in a common plane, said second plurality of passesbeing located in a common plane, said first and second plurality ofpasses being joined by return bend portions, each of said passes havinga plurality of fins thereon directed interiorly of said passes andhaving end portions thereon spaced apart from one another to form acentral opening through the center of said passes between said inlet andoutlet in said enclosure means, and means within said evaporatorcompartment for directing air from said enclosure means inlet throughsaid central opening, infrared heater means located interiorly of saidevaporator member, circuit means for selectively energizing saidinfrared heater means for defrosting said evaporator member, saidcircuit means including a thermostatically op erated switch forselectively connecting said infrared heater means across a power source,said thermally responsive means including a first bulb portion locatedin direct heat transfer relationship with said evaporator member and asecond serially connected bulb portion located in heat transferrelationship with air passing through said evaporator compartment inlet,said first bulb portion serving to initiate a defrost cycle of operationand said second bulb portion serving to terminate the defrost cycle ofoperation.

References Cited UNITED STATES PATENTS 2,068,435 1/1937 Rutishauser62-419 X 2,962,872 12/1960 Crotser 62-4l9 X 3,111,009 11/1963 Maudlin62l56 3,126,716 3/1964 De Witte 62419 X MEYER PERLIN, Primary Examiner.

1. A FROST-PROOF REFRIGERATOR COMPRISING INSULATING MEANS FORMING ABELOW-FREEZING COMPARTMENT AND AN ABOVE-FREEZING COMPARTMENT, ENCLOSUREMEANS FORMING AN EVAPORATOR COMPARTMENT SEPARATED FROM SAID FREEZINGCOMPARTMENTS INCLUDING AN INLET OPENING AND AN OUTLET OPENING, MEANS FORCIRCULATING AIR FROM SAID BELOW AND ABOVE-FREEZING COMPARTMENTS THROUGHSAID INLET OF SAID EVAPORATOR COMPARTMENT THENCE THROUGH THE OUTLET OFSAID EVAPORATOR COMPARTMENT, SAID FLUID CIRCULATING MEANS INCLUDING ARECIRCULATING FAN HAVING ITS INLET IN COMMUNICATION WITH THE OUTLET OFSAID EVAPORATOR COMPARTMENT, A HELICALLY COILED INTEGRAL FIN AND TUBEEVAPORATOR MEMBER LOCATED IN SAID EVAPORATOR COMPARTMENT BETWEEN THEINLET AND OUTLET ENDS THEREOF, SAID HELICALLY COILED EVAPORATOR MEMBERINCLUDING A FIRST PLURALITY OF PASSES LOCATED IN CLOSE SPACEDRELATIONSHIP WITH ONE SURFACE OF SAID EVAPORATOR ENCLOSURE MEANS AND ASECOND PLURALITY OF PASSES LOCATED IN CLOSE SPACED RELATIONSHIP WITHANOTHER SURFACE OF SAID EVAPORATOR ENCLOSURE MEANS, A PLURALITY OFRETURN BEND PORTIONS FOR JOINING SAID FIRST AND SECOND